Back pain takes an enormous toll on the health and productivity of people around the world. According to the American Academy of Orthopedic Surgeons, approximately 80 percent of Americans will experience back pain at some time in their life. In just the year 2000, approximately 26 million visits were made to physicians' offices due to back problems in the United States. On any one day, it is estimated that 5% of the working population in America is disabled by back pain.
Unfortunately, back pain is not only extremely common, but can also be difficult to accurately diagnose and effectively treat. Challenges stem from the fact that it is often difficult to pinpoint exactly what is causing a patient's pain or even where the pain originates. Although a number of effective treatments exist for various types of back pain, a number of them are highly invasive and may actually exacerbate pain or cause pain in other parts of the back. Therefore, due to the challenges involved in diagnosing and treating back pain, and fueled by the large number of patients suffering from back pain, improved diagnostic and treatment methods and devices and constantly being sought.
Back pain may be classified into two general categories: (1) “axial spinal pain,” which arises from pathology or dysfunction in the structural components of the spine, such as the vertebrae or the intervertebral discs between the vertebrae; and (2) “radicular pain,” which originates from pressure on or irritation of nerve roots. Radicular pain is often relatively simple to diagnose and pinpoint, because pain tends to radiate from irritated nerve roots out into the body in predictable patterns, and nerve root compression can often be seen on an MRI study or other radiological study of the spine. Treatment of radicular pain is also often quite straightforward, typically involving injections or surgical procedures procedures to decrease inflammation in or remove the structures impinging on the effected nerve root.
In contrast to radicular pain, axial spinal pain is typically much more difficult to diagnose and localize. “Discogenic pain,” for example, which is a type of spinal pain originating in one or more intervertebral discs (soft tissue structures between vertebrae of the spine), is particularly difficult to diagnose and pinpoint to one or more specific discs. The physical examination and complaints of the patient typically provide only general clues as to the actual cause and originating location of the pain, and no currently available radiological studies can accurately assess which of a patient's discs (if any) is causing discogenic pain. Adding to the difficulty of diagnosis is the fact that many different factors may lead to discogenic pain. Furthermore, it is often difficult to determine whether treatment of a disc (or discs) will actually alleviate the patient's pain or whether there are other underlying causes of the pain that will remain even after a disc is treated. Therefore, diagnosing and treating discogenic pain can often be incredibly challenging, and there is always a risk that surgery will be performed unnecessarily or will fail to relieve the patient's back pain.
The most commonly performed surgical procedure for treating discogenic pain is spinal fusion, in which adjacent vertebrae above and below the disc causing pain are fused together to prevent motion, thus bypassing the painful disc. Spinal fusion can be a very effective treatment, but it is relatively costly and invasive, and may be associated with a prolonged recovery and a number of potential complications. For example, fusion may sometimes lead to accelerated degeneration of one or more discs adjacent the treated disc due to increased forces placed on the adjacent discs from the fusion. Another possible treatment of discogenic pain involves replacement of the disc with an artificial (prosthetic) disc. This treatment may allow for better patient mobility than spinal fusion, but this treatment option is still in its infancy. Regardless of the method used to treat discogenic pain, an accurate diagnosis is essential for the treatment's success.
Despite the importance of obtaining a correct and specific diagnosis of discogenic pain, currently available diagnostic techniques have a number of drawbacks. A diagnostic test referred to as “discography” is the most commonly used and accepted diagnostic technique. Discography involves inserting a needle into an intervertebral disc and injecting a contrast dye into the compliant inner core of the disc (the nucleus pulposus) under pressure. A radiograph (or “X-ray”) of the spine is then taken. Sometimes, anatomical defects of the disc, such as tears in the fibrous outer layer of the disc (the annulus fibrosis) can been seen on a radiograph, which may be indicative of a possible cause of pain. Additionally, the injection of contrast into the disc under pressure has been shown to sometimes cause the patient to feel pain, caused by the chemical composition of the contrast and/or by increased pressure within the nucleus pulposus. Sometimes this pain mimics the back pain that the patient usually feels during daily activities. Through a combination of subjective analysis of radiographs and a subjective description of the back pain by the patient, the physician attempts to determine whether the particular disc is causing the patient's pain. In some instances, multiple discs on one patient are injected during a diagnostic procedure.
Some clinicians theorize that if a discogram is positive according to commonly used criteria, then the tested disc is the source of the patient's pain. However, there is no universally accepted definition of the criteria for a positive discogram. As a result, interpretation of discograms has been a longstanding controversy. Not only does the test rely on subjective feedback, but results themselves have been shown to have a high rate of false positives and false negatives, with up to 30-40% of patients with no back pain having positive discograms. Similarly, some patients have reported feeling a replication of their usual pain during discography, even though it is later found that another, non-discogenic cause was the actual origin of the pain. These facts demonstrate that the traditional discogram is not highly specific.
A number of currently available epidural catheters and techniques provide for injecting substances, typically anesthetics, into an epidural space of a spine. Examples of such epidural catheters are described in U.S. Pat. Nos. 3,885,561; 4,737,146; 4,973,305; 5,004,456; 5,024,655; 5,084,016; 5,129,889; 5,234,406; 5,344,439; 5,800,407; 6,676,643 and 6,368,315. Such catheters, however, are not adapted for delivery into an intervertebral disc. Furthermore, injecting substances into the epidural space is not helpful for diagnosing discogenic pain.
Due to the prevalence of discogenic pain and other types of back pain, the difficulty of accurately diagnosing and pinpointing discogenic pain, and the invasive nature of typical discogenic pain treatment techniques such as spinal fusion, improved methods and apparatus for diagnosing and/or treating discogenic pain are needed. Ideally, such methods and apparatus would enhance a physician's ability to pinpoint one or more discs that are causing a patient pain, thus enhancing or replacing traditional discography. Also ideally, these methods and devices would be no more invasive, or perhaps even less invasive, than discography. Even more ideally, variations of techniques and devices for diagnosing discogenic pain could also be used to treat back pain in some individuals, thus providing less invasive alternatives to traditional spinal fusion and other surgical techniques. At least some of these objectives will be met by the present invention.